P800 tax calculation: what the letter means, refund or underpayment, and how to check it
Got a P800 from HMRC? Why it was sent, how to check it against your P60, how a refund is paid and how an underpayment is collected through your tax code.
What the P800 is telling you
A P800 is HMRC's end-of-year check on the Income Tax taken through PAYE. After 5 April, HMRC compares the tax your employers and pension providers deducted with the tax it works out you owed. If the two do not match, it sends either a P800 "tax calculation letter" or a Simple Assessment letter, telling you how to get a refund or pay what you owe. You only get one if you are employed or get a pension; if you are registered for Self Assessment, your bill is adjusted instead and no letter is sent. The letters go out between June and March of the following tax year, so a P800 you receive during 2026/27 will normally be about 2025/26 (GOV.UK: tax overpayments and underpayments).
GOV.UK lists the usual reasons you get one, refund or bill:
- you were on the wrong tax code, for example because HMRC had the wrong information about your income;
- you finished one job, started a new one and were paid by both in the same month;
- you started receiving a pension at work;
- you received Employment and Support Allowance or Jobseeker's Allowance.
If you think you overpaid and no P800 has arrived, see our tax refund guide; if you think you owe tax and have had no letter, GOV.UK says to contact HMRC.
Is it real?
The P800 itself is a letter. HMRC says it may also send an email about a P800 refund if it has written to you and had no response, and that email will not ask for personal or financial information and will not contain links (HMRC: check if an email is genuine). A text or email with a "claim your refund" link is a scam. Do not use contact details from the message: sign in to your personal tax account or the HMRC app yourself. Our HMRC scams guide covers how to report one.
How to check the figures
A P800 is only as good as the figures HMRC holds, so check each one against your own records before you pay or spend a refund. The documents to hand (GOV.UK: your P45, P60 and P11D):
- P60 for each job you held on 5 April: the pay and tax for the whole tax year. You get a separate P60 for each job, and your employer must give it to you by 31 May.
- P45 for any job you left during the year: total pay and tax from 6 April to the date you left, and your tax code.
- P11D if you had company benefits, such as a car or medical insurance. A benefit that was never in your tax code is a common cause of an underpayment.
- Payslips, to check which tax code was used in which month.
Your personal tax account shows your income from work and the Income Tax you paid in the previous 5 years, and your tax code. If you cannot get a corrected P45, GOV.UK says to tell HMRC through its check your Income Tax online service and it will ask the employer for the correct details. Things to look for:
- every employer and pension is listed, and no job appears twice or belongs to someone else;
- the pay and tax for each one match your P60 or P45;
- any benefit included matches your P11D, and has not been counted for a period after it stopped;
- the allowances are the ones you are entitled to (for example, Marriage Allowance or a work-expenses claim).
Our guides to checking your tax code and P45, P60 and P11D forms go into each document in more detail.
If the P800 says you are due a refund
The letter says which of two routes applies (GOV.UK: if your P800 says you're due a refund):
| What the letter says | What you do | When the money arrives |
|---|---|---|
| You can claim online | Claim by bank transfer online, with the reference number from the letter and your National Insurance number. You can also claim through your personal tax account or the HMRC app (UK bank account needed), or by contacting HMRC. | Within 5 working days |
| You can claim online, and you ask for a cheque | Request the cheque online | Within 6 weeks |
| You will get a cheque | Nothing. The cheque is posted automatically; refunds for more than one year come as a single cheque. | Within 14 days of the date on the letter |
If the P800 says you owe tax
HMRC will usually collect it by changing your tax code, which increases the tax taken from your wages or pension, "usually in equal instalments for 12 months from the start of the following tax year". So a 2025/26 underpayment notified during 2026/27 is normally collected through your 2027/28 code, starting on 6 April 2027. GOV.UK says this happens automatically if you pay Income Tax through an employer or pension provider, earn enough over your Personal Allowance to cover the underpayment, and owe less than £3,000. If you prefer, you can pay what you owe before the start of the following tax year (GOV.UK: if your P800 says you owe tax).
The limits on coding it out
- Under £3,000. HMRC's PAYE Manual says only underpayments of up to £2,999.99 can be recovered through the tax code (PAYE90025, PAYE12070).
- The higher sliding scale is for other debts. Regulation 14D of the PAYE Regulations sets limits from £3,000 (expected PAYE income under £30,000) up to £17,000 (£90,000 or more) for debts such as unpaid Self Assessment tax and tax credit debts (SI 2003/2682 reg 14D). HMRC's manual says the sliding scale "do[es] not apply to SA balancing payments or PAYE underpayments" (PAYE14010), so it does not raise the P800 limit.
- Enough income, and not too much at once. HMRC should not code an underpayment where the income from that job or pension is not enough, where the 50% limit would be exceeded, or where it would double the tax deducted, a non-statutory safeguard HMRC can override at your request (PAYE12070). In GOV.UK's Simple Assessment example, tax equal to 50% of a private pension is "the maximum amount of tax that can be collected through your tax code" (GOV.UK: understand your Simple Assessment).
- The code cut is the tax divided by your rate. HMRC restricts your code by an amount based on the rate of tax you pay at your main job, so your tax-free amount falls by roughly the underpayment divided by that rate (see the worked example below; PAYE12080).
When it cannot go through your code: Simple Assessment
If the underpayment cannot be coded out, HMRC collects it through a Simple Assessment (form PA302, PAYE96345) instead (PAYE12080). GOV.UK lists owing £3,000 or more and owing tax that cannot be collected through your tax code among the reasons for one. The payment date is set by TMA 1970 s.59BA: 31 January after the end of the tax year, or 3 months after the notice if it is given after 31 October. You can query it within 60 days (s.31AA). Our Simple Assessment guide covers checking and paying it; if you cannot pay, see setting up Time to Pay.
Worked example: a benefit missing from the code
An employee in England earns £32,000 in 2025/26 on a standard cumulative code. Part-way through the year the employer starts paying for medical insurance, and the P11D after the year shows a taxable benefit of £600. The tax code was never changed to include it. Figures use the 2025/26 Personal Allowance of £12,570 and basic rate of 20% (England, Wales and Northern Ireland; a Scottish taxpayer's rates differ).
| Tax deducted through payroll: (£32,000 − £12,570) × 20% | £3,886 |
| Tax actually due: (£32,000 + £600 − £12,570) × 20% | £4,006 |
| Underpayment shown on the P800 | £120 |
| Reduction to the tax-free amount in the next code: £120 ÷ 20% | £600 |
| Extra tax each month over 12 months: £120 ÷ 12 | £10 |
The amount is under £3,000 and the employee earns well above the Personal Allowance, so it is coded out automatically. Payroll rounding means the real deductions can differ by a few pence. If the benefit continues, the new code should also include it; our guide to removing a benefit from your tax code covers the opposite case, where a benefit you no longer have is still in it.
If you think the P800 is wrong
- Tell HMRC which amounts are wrong and what they should be. If HMRC agrees, it sends a new calculation; if it disagrees, it contacts you to explain why (GOV.UK). Phone, digital assistant and online routes are on HMRC's Income Tax enquiries page, which lists "a P800 tax calculation" among the things to call about.
- Know what a P800 is in law. HMRC's manual describes it as "an informal calculation" with "no statutory force", and says HMRC needs to safeguard the tax where a customer challenges the calculation (PAYE93001). If HMRC then makes a formal assessment, you can appeal it in writing within 30 days of the notice (TMA 1970 s.31(1)(d) and s.31A). If it was collected by Simple Assessment, you must first query it within 60 days; HMRC's manual says an appeal against the revised bill must then be in writing within 30 days of the query closing (PAYE96345).
- If HMRC sat on information you or your employer gave it. Under Extra-Statutory Concession A19, arrears of Income Tax may be given up if they result from HMRC's failure to make proper and timely use of information from you, from your employer (where it affects your coding) or from DWP about certain pensions. Tax is normally given up only if you could reasonably have believed your affairs were in order and you were told of the arrears more than 12 months after the end of the tax year in which HMRC received the information (PAYE95005, text of ESC A19).
How far back HMRC can go, and how far back you can claim
- HMRC, ordinary case: 4 years. An assessment to Income Tax may be made "not more than 4 years after the end of the year of assessment to which it relates" (TMA 1970 s.34(1)). HMRC's manual says its time limit for issuing underpayment calculations is also 4 years (PAYE93001).
- HMRC, careless or deliberate: 6 or 20 years. The limit is 6 years where the loss of tax was brought about carelessly, and 20 years where it was brought about deliberately (TMA 1970 s.36(1) and (1A)).
- You: 4 years. No claim for relief may be made "more than 4 years after the end of the year of assessment to which it relates" (TMA 1970 s.43(1)). HMRC's manual adds that a claim counts from the date it is received, not when it is processed (PAYE93001). As of today, the oldest year you can still claim for is 2022/23, and the deadline for it is 5 April 2027.
Frequently asked questions
What is a P800 tax calculation?
A letter HMRC sends after the tax year ends (5 April) if you are employed or get a pension and paid too much or too little Income Tax through PAYE. It tells you how to get the refund or how the tax you owe will be paid. GOV.UK says the letters go out between June and March of the following tax year. If you are registered for Self Assessment you do not get one: your return is adjusted instead.
How long does a P800 refund take?
GOV.UK says that once you claim, the money is sent within 5 working days if you claimed online, or within 6 weeks if you asked HMRC to send a cheque. If the letter itself says you will get a cheque, you do not need to claim: it arrives within 14 days of the date on the letter.
How does HMRC collect a P800 underpayment?
Usually by changing your tax code, so the tax is collected in equal instalments over the 12 months from the start of the following tax year. GOV.UK says this happens automatically if you pay tax through an employer or pension, earn enough above your Personal Allowance to cover it, and owe less than £3,000. You can pay it yourself before that tax year starts instead.
What if I owe £3,000 or more?
HMRC's PAYE Manual (PAYE90025) says only underpayments of up to £2,999.99 can be recovered through the tax code. If the amount cannot be coded out, HMRC collects it through a Simple Assessment (a PA302) instead, which has its own payment deadline and a 60-day window to query it.
Is a P800 email or text from HMRC genuine?
HMRC says it may email to tell you about a P800 refund if it has sent you a letter and had no reply, but that email will not ask for personal or financial information and will not contain links. A message with a link to claim a refund is a scam. Claim only by signing in to your personal tax account or the HMRC app yourself.
What do I do if my P800 is wrong?
Contact HMRC and tell them which amounts you think are wrong and what they should be. If HMRC agrees, it sends a new calculation; if not, it contacts you to explain why. HMRC's own manual describes the P800 as an informal calculation with no statutory force.
How many years back can HMRC go, and how far back can I claim?
Under the Taxes Management Act 1970, an ordinary assessment and a claim for relief both have a 4-year limit from the end of the tax year (s.34 and s.43). HMRC can go back 6 years where you were careless and 20 years where you acted deliberately (s.36). HMRC says its own time limit for issuing underpayment calculations is 4 years.